Radio-Frequency Identification (RFID) relates to identification of objects by using electromagnetic radiation. RFID systems typically include two types of components, (1) RFID readers and (2) RFID tags.
RFID readers are transmitters of radio signals that are connected to external electric power sources. This power drives their antennas and creates radio waves. The RFID tags are integrated circuits that contain radio-frequency circuitry and information that identifies the tags. This invention is related to RFID systems in which tags communicate with the reader using the principle of backscatter modulation. When the radio waves transmitted by the reader are received by RFID tags, part of the received energy is reflected by the tags in a way that identifies the tag. The reader also acts as a radio receiver, and if it detects the reflected signal from the tag, the reader can identify the tag.
There are three desirable operations related to RFID systems: 1) object detection and identification, 2) accurate localization of the object upon detection and identification, and 3) tracking of the object if it is moving.
Current RFID systems can perform the task of object detection and identification but have difficulty with the remaining two tasks. In radio based communication systems, localization can be done using several established principles such as signals' time-of-arrivals (TOAs), time differences of arrivals (TDOAs), angle of arrivals (AOAs), or received signal strengths (RSSs).
However, implementation of these methods in RFID systems is extremely costly. Such systems require complex readers employing intensive signal processing and need for multiple antenna arrays. Additionally, for a typical RFID system the small distances between the reader and the tags cause difficulty in determining the range of the tag. The presence of multipath in indoor environments where RFID systems are most commonly used also causes errors in the calculation of the range.
Accordingly, there is a need to provide an RFID system that overcomes the aforementioned problems and can accurately locate and track an object with an RFID tag.